ABSTRACT
Demands on water resources for household, commercial, industrial, and agricultural purposes are increasing greatly. e world population will have grown 1.5 times over the second half of the twenty-rst century, but the worldwide water usage has been growing at more than three times the population growth. In most countries, human populations are growing while water availability is not. What is available for use, on a per capita basis, therefore, is falling. Out of 100 countries surveyed by the World Resources Institute in 1986, more than half of them were assessed to have low to very low water availability, and quality of water has been the key issue for the low water availability.
